Ensure culture-invariant date formatting for explicit formats and set test cultures

[Krishanthaudayakumara]

Description / Motivation

• Updated DateTagHelper to use CultureInfo.InvariantCulture when DateFormat is specified and no explicit Culture is set, ensuring consistent date output regardless of system locale.
• Explicitly set culture to en-US in RichTextFieldTagHelperFixture and other relevant integration test fixtures to make test expectations stable and independent of the developer's environment.
• Updated test assertions to use the correct culture where appropriate.
• Resolves test failures related to date formatting when running tests under non-US locales (e.g., da-DK).

Issue

encountered date formatting test failures when running the Sitecore ASP.NET Core SDK test suite with non-US locale settings (specifically Danish da-DK). The core issue was that date formatting was culture-dependent, causing tests to fail when the system culture used different date separators (dashes - vs slashes /).

Cause

DateTagHelper Implementation: Used CultureInfo.CurrentCulture for date formatting, making it dependent on system locale
Test Inconsistencies: Some tests expected invariant culture formatting while others expected current culture formatting
Integration Test Configuration: Missing explicit culture configuration in test fixtures, relying on system culture

Solution Implemented

1. Enhanced DateTagHelper Logic

string formattedDate = !string.IsNullOrWhiteSpace(DateFormat) ? field.Value.ToString(DateFormat, !string.IsNullOrWhiteSpace(Culture) ? culture : CultureInfo.InvariantCulture) : field.Value.ToString(culture);

Behavior

• When a specific DateFormat is provided (e.g., "MM/dd/yyyy"): Uses CultureInfo.InvariantCulture to ensure consistent formatting - regardless of system culture
• When a specific Culture is provided: Uses that culture as intended
• When no format is specified: Uses current culture for proper localization

2. Integration Test Culture Configuration

app.UseRequestLocalization(options =>
{
    var culture = new CultureInfo("en-US");
    options.DefaultRequestCulture = new RequestCulture(culture);
    options.SupportedCultures = [culture];
    options.SupportedUICultures = [culture];
});

Testing

• The Unit & Intergration tests are passing.
• I have added the necessary tests to cover my changes.

Terms

• I agree to follow this project's Code of Conduct.